The present invention relates to visual displays, and more particularly to addressable, reusable, paper-like visual displays, and to gyricon or twisting-ball displays.
Since ancient times, paper has been a preferred medium for the presentation and display of text and images. The advantages of paper as a display medium are evident. For example, it is lightweight, thin, portable, flexible, foldable, high-contrast, low-cost, relatively permanent, and readily configured into a myriad of shapes. It can maintain its displayed image without using any electricity. Paper can be read in ambient light and can be written or marked upon with a pen, pencil, paintbrush, or any number of other implements, including a computer printer.
Unfortunately, paper is not well suited for real-time display purposes. Real-time imagery from computer, video, or other sources cannot be displayed directly with paper, but must be displayed by other means, such as by a cathode-ray tube (CRT) display or a liquid-crystal display (LCD). Typically, real-time display media lack many of the desirable qualities of paper, such as physical flexibility and stable retention of the displayed image in the absence of an electric power source.
Attempts have been made to combine the desirable qualities of paper with those of real-time display media in order to create something that offers the best of both worlds. That something can be called electric paper.
Like ordinary paper, electric paper preferably can be written and erased, can be read in ambient light, and can retain imposed information in the absence of an electric field or other external retaining force. Also like ordinary paper, electric paper preferably can be made in the form of a lightweight, flexible, durable sheet that can be folded or rolled into tubular form about any axis and conveniently placed into a shirt or coat pocket, and then later retrieved, re-straightened, and read substantially without loss of information. Yet unlike ordinary paper, electric paper preferably can be used to display full-motion and other real-time imagery as well as still images and text. Thus it is adaptable for use in a computer system display screen or a television.
The gyricon, also called the twisting-ball display, rotary ball display, particle display, dipolar particle light valve, etc., offers a technology for making a form of electric paper. Briefly, a gyricon is an addressable display made up of a multiplicity of optically anisotropic balls, each of which can be selectively rotated to present a desired face to an observer. For example, a gyricon can incorporate balls each having two distinct hemispheres, one black and the other white, with each hemisphere having a distinct electrical characteristic (e.g., zeta potential with respect to a dielectric fluid) so that the balls are electrically as well as optically anisotropic. The black-and-white balls are embedded in a sheet of optically transparent material, such as an elastomer layer, that contains a multiplicity of spheroidal cavities and is permeated by a transparent dielectric fluid, such as a plasticizer. The fluid-filled cavities accomodate the balls, one ball per cavity, so as to prevent the balls from migrating within the sheet. A ball can be selectively rotated within its respective fluid-filled cavity, for example by application of an electric field, so as to present either the black or the white hemisphere to an observer viewing the surface of the sheet. Thus, by application of an electric field addressable in two dimensions (as by a matrix addressing scheme), the black and white sides of the balls can be caused to appear as the image elements (e.g., pixels or subpixels) of a displayed image.
The gyricon is described further in the patents incorporated by reference hereinabove. In particular, U.S. Pat. No. 5,389,945 (Sheridon, xe2x80x9cWriting System Including Paper-Like Digitally Addressed Media and Addressing Device Thereforxe2x80x9d) shows that gyricon displays can be made that have many of the desirable qualities of paper, such as flexibility and stable retention of a displayed image in the absence of power, not found in CRTs, LCDs, or other conventional display media. Gyricon displays can also be made that are not paper-like, for example, in the form of rigid display screens for flat-panel displays.
Although the gyricon represents an important step toward the goal of electric paper, there is still a long way to go. For example, a gyricon constructed of black-and-white balls cannot provide a multicolor image. As another example, a gyricon designed to operate in ambient reflected light cannot provide a projective or transmissive display. What is needed is an advanced gyricon technology that can provide a more full range of display capabilities while preserving paper-like advantages.
GOODRICH (U.S. Pat. No. 4,261,653, xe2x80x9cLight Valve Including Dipolar Particle Construction and Method of Manufacturexe2x80x9d) discloses a light valve based on a spherical ball that can be rotated between a first orientation and a second orientation through the application of oscillating electric fields of two different frequencies. Goodrich""s spherical ball is made up of a light-absorptive or light-reflective central segment surrounded by transparent intermediate and outer segments. In the first orientation of the ball, the central segment is transverse to the direction of incident light and so blocks the passage of light. In the second orientation of the ball, the central segment is aligned with the direction of incident light and so admits the passage of light, which passes through the transparent portions of the ball. Rotation between the first and second orientations is accomplished by changing the frequency of an applied oscillating electric field from a high frequency (e.g., 10,000 Hz) to a low frequency (e.g., 100 Hz), and taking advantage of the frequency-dependent dielectric characteristics of the intermediate segments and the frequency-insensitive dielectric characteristics of the outer segments. When the frequency of the applied field is high, the dielectric constant of the intermediate segments becomes less than that of the outer segments, and the induced charge in the intermediate segments causes the ball to orient in the first orientation. When the frequency of the applied field is low, the dielectric constant of the intermediate segments becomes greater than that of the outer segments, and the induced charge in the intermediate segments causes the ball to orient in the second orientation.
Goodrich""s frequency-dependent addressing scheme requires specialized, possibly cumbersome addressing electronics and an AC voltage source capable of delivering high frequencies (e.g., RF frequencies). Goodrich""s light valve balls (although said by Goodrich to be xe2x80x9cdipolarxe2x80x9d) would not be responsive to a change in orientation of the electric field vector of a steady-state, nonoscillating electric field. Thus Goodrich""s overall approach does not appear to be readily adaptable for use with electric fields produced from a simple DC voltage source without transformation to high-frequency AC.
According to the invention, a material suitable for use as a gyricon sheet is provided. The material is composed of a substrate in which first and second kinds of spheroidal balls are disposed. Each ball of the first kind has a first collection of physical characteristics, and each ball of the second kind has a second collection of physical characteristics, such that spheroidal balls of the second kind are thus physically distinguishable from spheroidal balls of the first kind. Each ball of each kind has an optical anisotropy and an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in an electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field.
In another aspect, a method of making a product comprising optically anisotropic spheroidal balls disposed in a substrate, as for a gyricon, is provided. According to the method, a receiving surface comprising a material in an adhesive state is provided. First and second sets of spheroidal balls are deposited on the receiving surface, each of the first and second sets comprising at least one ball, the spheroidal balls thus deposited adhering to the receiving surface material in the adhesive state. For example, balls of the first set can be deposited in a first arrangement on the receiving surface, and balls of the second set can be deposited in a second arrangement on the receiving surface. Each ball of the first set has a first collection of physical characteristics, and each ball of the second set has a second collection of physical characteristics, balls of the second set thus being physically distinguishable from balls of the first set. Each ball of each set has an optical anisotropy and an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in an electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field. A material in a pourable state is deposited on the receiving surface and over the spheroidal balls adhering to the receiving surface material, thereby covering the spheroidal balls adhering to the receiving surface material and thus forming an uncured substrate material wherein the balls of the first and second sets are disposed, the uncured substrate material comprising the receiving surface material in the adhesive sate and the material deposited in the pourable state. At least a portion of the uncured substrate material is cured to a nonadhesive, nonpourable state with the spheroidal balls of the first and second sets thus disposed therein, so as to form a substrate in which are disposed at least one spheroidal ball of the first set and at least one spheroidal ball of the second set. Optionally, a fluid, such as a plasticizer fluid, can be applied to the substrate thus formed, thereby expanding the substrate so as to render at least one spheroidal ball disposed in the substrate rotatable within the substrate.
In still another aspect of the invention, a method is provided for making a gyricon substrate. According to the method, a receiving surface comprising a material in an adhesive state is provided. A set of spheroidal balls is selectively deposited on the receiving surface, the set including at least one ball. Each ball of the set has an optical anisotropy and an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in an electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field. Each ball of the set thus selectively deposited is deposited at one of a first plurality of locations on the receiving surface, while substantially none of the spheroidal balls of the set thus deposited are deposited at any of a second plurality of locations on the receiving surface, the second set of locations thus being maintained substantially free of balls of the set thus deposited. The spheroidal balls thus selectively deposited adhere to the receiving surface material in the adhesive state. A material in a pourable state is deposited on the receiving surface and over the spheroidal balls adhering to the receiving surface material, thereby covering the spheroidal balls adhering to the receiving surface material and thus forming an uncured substrate material wherein the balls of the set are disposed. This uncured substrate material includes the receiving surface material in the adhesive state and the material deposited in the pourable state. At least a portion of the uncured substrate material is cured to a nonadhesive, nonpourable state with the spheroidal balls of the set thus disposed therein, thereby forming a substrate in which at least one spheroidal ball of the set is disposed. Each spheroidal ball of the set thus disposed in the substrate is disposed in a vicinity of a location in the substrate corresponding to one of the first plurality of locations on the receiving surface. The substrate thus formed further includes at least one location, corresponding to one of the second plurality of locations on the receiving surface, in which substantially no spheroidal balls of the set are disposed.
In yet another aspect of the invention, a nonfusing xerographic apparatus suitable for placing balls in a gyricon sheet is provided. The apparatus includes a charge receptor member, means for creating an electrostatic latent image on the charge receptor member, means for developing the electrostatic latent image, and means for transferring the image thus developed onto an adhesive receiving surface. The means for developing comprises means for electrostatically depositing a toner medium on the charge receptor member, the toner medium including a plurality of particles. The particles are made up of spheroidal balls, each ball having an optical anisotropy and an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in an electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field.
In yet still another aspect of the invention, a toner medium for use in a nonfusing xerographic process is provided. The toner medium is composed of magnetic particles and spheroidal ball particles, each of the latter including a spheroidal ball. Each spheroidal ball has an optical anisotropy and an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the spheroidal ball electrically responsive such that when the ball is rotatably disposed in an electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field.
The invention will be better understood with reference to the drawings and detailed description below. In the drawings, like reference numerals indicate like components.